Aluminum base alloy



elevated 'temperatures.

' Patented Oct. 9, 1945 ALUMINUM BASE ALLOY La Verne W. Eastwood, University Heights, Ohio, assignor to Aluminum Company of America, Pittsburgh, Pa., a corporation of Pennsylvania No Drawing.

Application December 24, 1942, Serial N0. 470,095

3 Claims. (01. 75-142) This invention relates to aluminum base alloys suitable for making castings, the principal object of the invention being the provision of an alloy composition which is adapted for use at elevated temperatures such as are encountered in internal combustion engines. The particular object is to provide an alloy which'possesses a relatively high tensile. strength and resistance to fatigue at .elevated temperatures.

Although there are numerous aluminum base alloys that serve satisfactorily at room temperature, there are relatively few that possess properties required for extended service at elevated temperatures. One of the compositions which has been widely used for this purpose and which may be considered as being typical of this kind of aluminum base alloy is one having tlie nominal composition of 4 per cent copper, 1.5 per cent magnesium, 2 per cent nickel, balance aluminum. This composition is generally known as the Y alloy. This alloy has found extensive employment in the manufacture of pistons, cylinder heads and other parts of internal combustion engines subjected to The satisfactory performance of this alloy under such conditions is attributable in large part to the nickel component. 1

Because of the commercial scarcity of this element under current conditions, it is highly desirable to have an alloy possessing the properties of the Y alloy which does not require the presence of nickel; As a result of an extended investigation along this line, I have now discovered that a nickel-free aluminum base alloy containing from about 3 to 5 per cent copper, 1 to 2 per cent magnesium, and 1.5 to 3.0 per cent iron as the principal added alloying elements can be successfully employed for high temperature applications because of its relatively high strength and endurance limit at elevated temperatures. By relatively high strength and endurance limit at elevated temperatures I mean that the values for these properties exceed those for most commercial aluminum base alloys and are substantially equal to those of the aforesaid Y alloy at the same temperature- .I have found, moreover, that nickel is deleterious in my alloy and must be kept below 0.5 per cent, and preferably should be excluded entirely where possi 1e.

The behavior .of such a large concentration of iron in-the alloy is quite remarkable in view of the known characteristic of this element in forming a brittle intermetallic compound FeAla' which generally renders the alloy brittle where it occurs. In my nickel-free alloy', however, the iron constituent is uniformly distributed so that the tle and the casting properties are not satisfactory above-mentioned range is illustrated in the following tensile tests at 500 and 600 P. where they were compared with the Y alloy. Standard tensile test bars of'each of the alloys were cast in a conventional green sand mold. The copper, magnesium, nickel and iron contents of the alloys are given in Table I, the balance of the alloys being aluminum and impurities. The Y alloy specimens had an. iron impurity content of about 0.5 per cent which is normal for this alloy. Test bars of all the alloys were first annealed at 700 F. for 12 hours and cooled to room temperature to render them structurally stable at the subsequent testing temperature. were then broken in tension at 600 F. after'hav-i ing been held at this temperature for /2' hour. The average tensile properties of the test bars are given-in Table I.'

TABLE I Tensile properties at 500 and 600 F.

The behavior of two of my alloys within the The bars" Alloy composition Temp. Tensile P of test, strengtl1,lbs./ g g Percent Percent Percent F. sq. in. a Mg Ni Fe The above test results clearly show that the tensile strengths of the two alloys are substantially equal at the elevated temperatures. The range in variation of elongation values is not unusual for cast alloys tested at 500 and 600 F.

and hence the differences between individual" tests-are not to be considered as significant.

The endurance limits of Y alloy and one of my compositions at 500 F. are illustrated in the following test. Sand cast tensile test bars were iven a solution heat treatment at 960 F. followed by quenching in air and aging at 600 F. for 2 hours before being heated to the testing temperature. of 500 F. The preliminary thermal treatment duplicated the treatment frequently given to Y alloy castings prior to being 5 placed in service at elevated temperatures. The test bars were subjected to alternating stresses for 500,000,000 cycles at the elevated temperature on the well knowncantilever type of fatigue testing machine. The nominal alloy com- 1 positions, with the exception of the aluminum component and impurities, and the endurance limits are given in Table 11 below.

' TABLE II Endurance limit at 500 F.

From these results it is apparent that both alloys have the same endurance limit at the same elevated temperature.

* Although favorable'properties are obtained at elevated temperatures within the broad range previously mentioned, I have found that the best combination of properties occur in alloys containing from 3.4 to 4.5 per cent copper, 1.2 to 1.8 per cent magnesium and 1.8 to 2.6 per cent iron. .In some instances it maybe desirable to include other elements in the alloys within either the broad or preferred ranges to enhance particular properties, such as refinement of grain, or resistance to corrosion. For this purpose at least one of the group of such so-called hardening elements as chromium, titanium, boron, and

the like, may be added in the following amounts,

0.01 to 0.2 per cent'chromium, 0.002 to 0.2 per" cent titanium, 0.001 to 0.04 per cent boron. The

total amount of these elements should not, in

general, execeed about 1.0 per cent.

While the alloy may be employed to make castings, it can also be fabricated into wrought products similar to those produced in .Y alloy.

It finds particular application in making sand and semi-permanent mold castings.

The usual impurities occurring in aluminum or secondary metal can be tolerated in my improved alloy within certain Silicon, for

Alloy composition Lbs.[sq. in. Percent Percent Percent Percent 20 Cu Mg Ni Fe 4.0 1. 5 2. 3 5, 000 4. o 1. a 2. o 5, 000

and if more than 1 per cent is present, the strength is decreased to a point where the alloy would be considered unsuitable as a substitute for Y. alloy in many commercial applications. Nickel may also appear as an impurity when secondary metal is employed, and where this happens the amount should not exceed 0.5 per cent since larger amounts are deleterious to the microstructure of the alloy. Alloys containing less than 0.5 per cent nickel are herein ccnsidered to be nickel-free. Still another impurity which may appear in the alloy is zinc, and this element likewise should be kept below 0.5 per cent. Other impurities may be found in the alloy but in no case should they or any of the aforementioned impurities be present in such amounts as to substantially impair the strength of the alloy at elevated temperatures.

In the appended claims where the balance of the alloy is said to be substantially aluminum it is to. be understood that this includes bothftheimpurities and the hardening elements mentioned hereinabove. The elements copper, magnesium and iron are considered to be the chief elements which in combination with aluminum produce an alloy adapted for service at elevated temperatures.

Having thus described my invention and-certain embodiments thereof,

I claim:

1. A nickel-free aluminum base alloy containing from 3.0 to 5.0 per cent copper, 1.0 to 2.0 per cent magnesium, 1.5 to 3.0 per cent iron, less than 0.5 per cent silicon impurity, and the balance substantially aluminum, said alloy being characterized by a relatively high tensile strength and resistance to fatigue at elevated temperatures.

2. A-nickel-free aluminum base alloy contain- 0 ing 3.4 to 4.5 per cent copper, 1.2 to 1.8 per cent magnesium, 1.8 to 2.6 per cent iron, less than 0.5 per cent silicon impurity, and the balance substantially aluminum, said alloy being characterized by a relatively high tensile strength and resistance to fatigue at elevated temperatures.

3. A nickel-free aluminum base alloy consisting of from 3 to 5 per cent copper, 1.0 to 2.0 per cent magnesium, 1.5 to 3.0 per cent iron, less than 0.5 per cent silicon impurity, at least one of the group of hardening elements composed of 0.01 to 0.2 per cent chromium, 0.002 to 0.2 per cent titanium and 0.001 to 0.04 per cent boron, and the balance aluminum, said alloy being characterized by a relatively high tensile strength example, should not exceed about 1 per cent and 5 and resistance to fatigue at elevated temperapreferabLv should be less than 0.5 per cent since it reduces the strength at elevated temperatures,

tures.

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